The present invention is generally directed to toner charging apparatuses, and more specifically, the present invention is directed to a toner charging apparatus containing coated toner transporting members. The apparatus of the present invention is useful in a number of imaging processes including electrostatographic imaging systems comprised, in operative relationship, of a means for simultaneously metering and charging nonmagnetic insulating toner particles.
The development of images by various methods, including electrostatographic means, is well known. In several of these methods, toner particles are deposited on an electrostatic latent image present on an insulating surface, such as selenium, utilizing, for example, cascade development, magnetic brush development, powder cloud development, and touchdown development. In view of several disadvantages associated with two-component systems, considerable effort has been directed to designing processes which utilize toner particles only, reference for example U.S. Pat. No. 2,846,333. This patent discloses a single component developer composition comprised of toner resins, colorants, and magnetic materials.
In many of the single component development processes, conductive toner particles are selected, and imagewise toner deposition onto the photoconductive member is obtained by induction charging of the toner particles. Electrostatic transfer of conductive toner particles of plain bond paper is, however, usually inefficient as the charge on the toner particles can be reversed by induction charging from the paper during the transfer step. Accordingly, electrophotographic systems wherein conductive single component toner particles are used can require a special overcoated insulating paper to achieve sufficient electrostatic toner transfer. Furthermore, in single component processes with conductive toner particles the control of undesirable background, or background suppression, cannot usually be achieved with electrostatic forces as the toner particles are inductively charged, and deposited on the image bearing member, which is not the situation with two-component developer processes where control of background development is accomplished by electrostatic forces acting on the triboelectrically charged toner particles, causing these particles to be directed away from image bearing members.
Recently, there has been disclosed an efficient, single component, economical, simple process, and apparatus for the development of latent electrostatic images wherein insulative, nonmagnetic, or color toner particles are appropriately charged; and there is obtained two-component image quality utilizing a single component development apparatus. In this system, as detailed hereinafter, and as described in U.S. Pat. No. 4,459,009, the disclosure of which is totally incorporated herein by reference, there is selected a charging roll means which simultaneously meters and charges toner particles. A donor electrode serves to transport the toner particles, which electrode can be comprised of numerous suitable materials, including for example, aluminized Mylar overcoated with a polymer containing carbon black, electroformed nickel, or a carbon black loaded extruded polymer. While these materials may be satisfactory for their intended purposes, there continues to be a need for new coatings wherein the surface topography thereof is stable, and textured to assist in the transporting of toner particles from the donor electrode to the imaging member.
Furthermore, known prior art coatings such as Krylon coated onto a nickel substrate, although suitable for their intended purposes, are not scratch resistant over extended time periods. Thus, these coatings permit scratches to form on the toner transporting means, which in turn adversely affects image copy quality. Additionally, toner particles appear to permanently adhere to the surface of transporting members with Krylon coatings, which adhesion results in undesirable high background deposits on the resulting developed images.
There is also described in U.S. Pat. No. 4,505,573, the disclosure of which is totally incorporated herein by reference, a transporting means for insulating toner particles comprised of a suitable substrate and a coating thereover of a low surface energy, wear resistant material. More specifically, there is disclosed in this patent application an insulating toner transporting system comprised of a substrate, and a coating thereover of a fluoropolymer. The improved toner transporting means of '573 are particularly useful in an apparatus for charging toner particles comprised in operative relationship of a means for charging insulating toner particles, and a means for transporting insulating toner particles wherein the means for charging and the means for transporting are biased to a predetermined potential.
Accordingly, in one embodiment, the invention of the referred to copending application is directed to an apparatus for a charging insulating toner particles comprised, in operative relationship, of a means for charging insulating toner particles; and a means for transporting insulating toner particles, the means for charging and the means for transporting being biased to a predetermined potential wherein the transporting means contains a mixture of a fluoropolymer coating, and conductive particles such as carbon black. In accordance with the present invention, alternative coatings for the transporting means are provided.